Perhaps to get the ball rolling, I can offer what I have read, mostly.
Protein is good, so is calcium (if I recall correctly, ducks need three times the calcium while they are laying).
Light has something to do with laying, too. (Side trip: I will be managing my flock of runners to lay seasonally, so the light they have will be mostly normal daylight. i don't expect them to lay year 'round. I want them to have some rest. And with ducks that lay about two hundred eggs each per year (during optimum laying years), who needs to try to max them out?)
Back to light and ducks in general. I believe I read that fourteen hours of light a day (doesn't have to be really bright light at all) helps optimize laying. But as to when she will be laying, if her body is not ready for some reason, I would take a careful look at her overall health and her environment, and what has changed for her since she was laying. That includes body condition, temperatures (too much heat can stress as much as too much cold), availability of water and protein and calories and calcium, among other things, stress level (what has changed? New animals? New housing? Loss of a flockmate?), recent or undiagnosed illness or injury.
I hope some of these musings can give you a clue, and that someone with more experience chimes in soon.
